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| -rw-r--r-- | MAINTAINERS | 2 | ||||
| -rw-r--r-- | docs/devel/index-internals.rst | 1 | ||||
| -rw-r--r-- | docs/devel/s390-cpu-topology.rst | 170 | ||||
| -rw-r--r-- | docs/system/s390x/cpu-topology.rst | 244 | ||||
| -rw-r--r-- | docs/system/target-s390x.rst | 1 | ||||
| -rw-r--r-- | qapi/machine.json | 2 |
6 files changed, 420 insertions, 0 deletions
diff --git a/MAINTAINERS b/MAINTAINERS index cfc37e9..de8d9f5 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -1716,6 +1716,8 @@ S: Supported F: include/hw/s390x/cpu-topology.h F: hw/s390x/cpu-topology.c F: target/s390x/kvm/stsi-topology.c +F: docs/devel/s390-cpu-topology.rst +F: docs/system/s390x/cpu-topology.rst X86 Machines ------------ diff --git a/docs/devel/index-internals.rst b/docs/devel/index-internals.rst index e1a93df..6f81df9 100644 --- a/docs/devel/index-internals.rst +++ b/docs/devel/index-internals.rst @@ -14,6 +14,7 @@ Details about QEMU's various subsystems including how to add features to them. migration multi-process reset + s390-cpu-topology s390-dasd-ipl tracing vfio-migration diff --git a/docs/devel/s390-cpu-topology.rst b/docs/devel/s390-cpu-topology.rst new file mode 100644 index 0000000..9eab28d --- /dev/null +++ b/docs/devel/s390-cpu-topology.rst @@ -0,0 +1,170 @@ +QAPI interface for S390 CPU topology +==================================== + +The following sections will explain the QAPI interface for S390 CPU topology +with the help of exemplary output. +For this, let's assume that QEMU has been started with the following +command, defining 4 CPUs, where CPU[0] is defined by the -smp argument and will +have default values: + +.. code-block:: bash + + qemu-system-s390x \ + -enable-kvm \ + -cpu z14,ctop=on \ + -smp 1,drawers=3,books=3,sockets=2,cores=2,maxcpus=36 \ + -device z14-s390x-cpu,core-id=19,entitlement=high \ + -device z14-s390x-cpu,core-id=11,entitlement=low \ + -device z14-s390x-cpu,core-id=112,entitlement=high \ + ... + +Additions to query-cpus-fast +---------------------------- + +The command query-cpus-fast allows querying the topology tree and +modifiers for all configured vCPUs. + +.. code-block:: QMP + + { "execute": "query-cpus-fast" } + { + "return": [ + { + "dedicated": false, + "thread-id": 536993, + "props": { + "core-id": 0, + "socket-id": 0, + "drawer-id": 0, + "book-id": 0 + }, + "cpu-state": "operating", + "entitlement": "medium", + "qom-path": "/machine/unattached/device[0]", + "cpu-index": 0, + "target": "s390x" + }, + { + "dedicated": false, + "thread-id": 537003, + "props": { + "core-id": 19, + "socket-id": 1, + "drawer-id": 0, + "book-id": 2 + }, + "cpu-state": "operating", + "entitlement": "high", + "qom-path": "/machine/peripheral-anon/device[0]", + "cpu-index": 19, + "target": "s390x" + }, + { + "dedicated": false, + "thread-id": 537004, + "props": { + "core-id": 11, + "socket-id": 1, + "drawer-id": 0, + "book-id": 1 + }, + "cpu-state": "operating", + "entitlement": "low", + "qom-path": "/machine/peripheral-anon/device[1]", + "cpu-index": 11, + "target": "s390x" + }, + { + "dedicated": true, + "thread-id": 537005, + "props": { + "core-id": 112, + "socket-id": 0, + "drawer-id": 3, + "book-id": 2 + }, + "cpu-state": "operating", + "entitlement": "high", + "qom-path": "/machine/peripheral-anon/device[2]", + "cpu-index": 112, + "target": "s390x" + } + ] + } + + +QAPI command: set-cpu-topology +------------------------------ + +The command set-cpu-topology allows modifying the topology tree +or the topology modifiers of a vCPU in the configuration. + +.. code-block:: QMP + + { "execute": "set-cpu-topology", + "arguments": { + "core-id": 11, + "socket-id": 0, + "book-id": 0, + "drawer-id": 0, + "entitlement": "low", + "dedicated": false + } + } + {"return": {}} + +The core-id parameter is the only mandatory parameter and every +unspecified parameter keeps its previous value. + +QAPI event CPU_POLARIZATION_CHANGE +---------------------------------- + +When a guest requests a modification of the polarization, +QEMU sends a CPU_POLARIZATION_CHANGE event. + +When requesting the change, the guest only specifies horizontal or +vertical polarization. +It is the job of the entity administrating QEMU to set the dedication and fine +grained vertical entitlement in response to this event. + +Note that a vertical polarized dedicated vCPU can only have a high +entitlement, giving 6 possibilities for vCPU polarization: + +- Horizontal +- Horizontal dedicated +- Vertical low +- Vertical medium +- Vertical high +- Vertical high dedicated + +Example of the event received when the guest issues the CPU instruction +Perform Topology Function PTF(0) to request an horizontal polarization: + +.. code-block:: QMP + + { + "timestamp": { + "seconds": 1687870305, + "microseconds": 566299 + }, + "event": "CPU_POLARIZATION_CHANGE", + "data": { + "polarization": "horizontal" + } + } + +QAPI query command: query-s390x-cpu-polarization +------------------------------------------------ + +The query command query-s390x-cpu-polarization returns the current +CPU polarization of the machine. +In this case the guest previously issued a PTF(1) to request vertical polarization: + +.. code-block:: QMP + + { "execute": "query-s390x-cpu-polarization" } + { + "return": { + "polarization": "vertical" + } + } diff --git a/docs/system/s390x/cpu-topology.rst b/docs/system/s390x/cpu-topology.rst new file mode 100644 index 0000000..5133fdc --- /dev/null +++ b/docs/system/s390x/cpu-topology.rst @@ -0,0 +1,244 @@ +.. _cpu-topology-s390x: + +CPU topology on s390x +===================== + +Since QEMU 8.2, CPU topology on s390x provides up to 3 levels of +topology containers: drawers, books and sockets. They define a +tree-shaped hierarchy. + +The socket container has one or more CPU entries. +Each of these CPU entries consists of a bitmap and three CPU attributes: + +- CPU type +- entitlement +- dedication + +Each bit set in the bitmap correspond to a core-id of a vCPU with matching +attributes. + +This documentation provides general information on S390 CPU topology, +how to enable it and explains the new CPU attributes. +For information on how to modify the S390 CPU topology and how to +monitor polarization changes, see ``docs/devel/s390-cpu-topology.rst``. + +Prerequisites +------------- + +To use the CPU topology, you need to run with KVM on a s390x host that +uses the Linux kernel v6.0 or newer (which provide the so-called +``KVM_CAP_S390_CPU_TOPOLOGY`` capability that allows QEMU to signal the +CPU topology facility via the so-called STFLE bit 11 to the VM). + +Enabling CPU topology +--------------------- + +Currently, CPU topology is only enabled in the host model by default. + +Enabling CPU topology in a CPU model is done by setting the CPU flag +``ctop`` to ``on`` as in: + +.. code-block:: bash + + -cpu gen16b,ctop=on + +Having the topology disabled by default allows migration between +old and new QEMU without adding new flags. + +Default topology usage +---------------------- + +The CPU topology can be specified on the QEMU command line +with the ``-smp`` or the ``-device`` QEMU command arguments. + +Note also that since 7.2 threads are no longer supported in the topology +and the ``-smp`` command line argument accepts only ``threads=1``. + +If none of the containers attributes (drawers, books, sockets) are +specified for the ``-smp`` flag, the number of these containers +is 1. + +Thus the following two options will result in the same topology: + +.. code-block:: bash + + -smp cpus=5,drawer=1,books=1,sockets=8,cores=4,maxcpus=32 + +and + +.. code-block:: bash + + -smp cpus=5,sockets=8,cores=4,maxcpus=32 + +When a CPU is defined by the ``-smp`` command argument, its position +inside the topology is calculated by adding the CPUs to the topology +based on the core-id starting with core-0 at position 0 of socket-0, +book-0, drawer-0 and filling all CPUs of socket-0 before filling socket-1 +of book-0 and so on up to the last socket of the last book of the last +drawer. + +When a CPU is defined by the ``-device`` command argument, the +tree topology attributes must all be defined or all not defined. + +.. code-block:: bash + + -device gen16b-s390x-cpu,drawer-id=1,book-id=1,socket-id=2,core-id=1 + +or + +.. code-block:: bash + + -device gen16b-s390x-cpu,core-id=1,dedicated=true + +If none of the tree attributes (drawer, book, sockets), are specified +for the ``-device`` argument, like for all CPUs defined with the ``-smp`` +command argument the topology tree attributes will be set by simply +adding the CPUs to the topology based on the core-id. + +QEMU will not try to resolve collisions and will report an error if the +CPU topology defined explicitly or implicitly on a ``-device`` +argument collides with the definition of a CPU implicitly defined +on the ``-smp`` argument. + +When the topology modifier attributes are not defined for the +``-device`` command argument they takes following default values: + +- dedicated: ``false`` +- entitlement: ``medium`` + + +Hot plug +++++++++ + +New CPUs can be plugged using the device_add hmp command as in: + +.. code-block:: bash + + (qemu) device_add gen16b-s390x-cpu,core-id=9 + +The placement of the CPU is derived from the core-id as described above. + +The topology can of course also be fully defined: + +.. code-block:: bash + + (qemu) device_add gen16b-s390x-cpu,drawer-id=1,book-id=1,socket-id=2,core-id=1 + + +Examples +++++++++ + +In the following machine we define 8 sockets with 4 cores each. + +.. code-block:: bash + + $ qemu-system-s390x -m 2G \ + -cpu gen16b,ctop=on \ + -smp cpus=5,sockets=8,cores=4,maxcpus=32 \ + -device host-s390x-cpu,core-id=14 \ + +A new CPUs can be plugged using the device_add hmp command as before: + +.. code-block:: bash + + (qemu) device_add gen16b-s390x-cpu,core-id=9 + +The core-id defines the placement of the core in the topology by +starting with core 0 in socket 0 up to maxcpus. + +In the example above: + +* There are 5 CPUs provided to the guest with the ``-smp`` command line + They will take the core-ids 0,1,2,3,4 + As we have 4 cores in a socket, we have 4 CPUs provided + to the guest in socket 0, with core-ids 0,1,2,3. + The last CPU, with core-id 4, will be on socket 1. + +* the core with ID 14 provided by the ``-device`` command line will + be placed in socket 3, with core-id 14 + +* the core with ID 9 provided by the ``device_add`` qmp command will + be placed in socket 2, with core-id 9 + + +Polarization, entitlement and dedication +---------------------------------------- + +Polarization +++++++++++++ + +The polarization affects how the CPUs of a shared host are utilized/distributed +among guests. +The guest determines the polarization by using the PTF instruction. + +Polarization defines two models of CPU provisioning: horizontal +and vertical. + +The horizontal polarization is the default model on boot and after +subsystem reset. When horizontal polarization is in effect all vCPUs should +have about equal resource provisioning. + +In the vertical polarization model vCPUs are unequal, but overall more resources +might be available. +The guest can make use of the vCPU entitlement information provided by the host +to optimize kernel thread scheduling. + +A subsystem reset puts all vCPU of the configuration into the +horizontal polarization. + +Entitlement ++++++++++++ + +The vertical polarization specifies that the guest's vCPU can get +different real CPU provisioning: + +- a vCPU with vertical high entitlement specifies that this + vCPU gets 100% of the real CPU provisioning. + +- a vCPU with vertical medium entitlement specifies that this + vCPU shares the real CPU with other vCPUs. + +- a vCPU with vertical low entitlement specifies that this + vCPU only gets real CPU provisioning when no other vCPUs needs it. + +In the case a vCPU with vertical high entitlement does not use +the real CPU, the unused "slack" can be dispatched to other vCPU +with medium or low entitlement. + +A vCPU can be "dedicated" in which case the vCPU is fully dedicated to a single +real CPU. + +The dedicated bit is an indication of affinity of a vCPU for a real CPU +while the entitlement indicates the sharing or exclusivity of use. + +Defining the topology on the command line +----------------------------------------- + +The topology can entirely be defined using -device cpu statements, +with the exception of CPU 0 which must be defined with the -smp +argument. + +For example, here we set the position of the cores 1,2,3 to +drawer 1, book 1, socket 2 and cores 0,9 and 14 to drawer 0, +book 0, socket 0 without defining entitlement or dedication. +Core 4 will be set on its default position on socket 1 +(since we have 4 core per socket) and we define it as dedicated and +with vertical high entitlement. + +.. code-block:: bash + + $ qemu-system-s390x -m 2G \ + -cpu gen16b,ctop=on \ + -smp cpus=1,sockets=8,cores=4,maxcpus=32 \ + \ + -device gen16b-s390x-cpu,drawer-id=1,book-id=1,socket-id=2,core-id=1 \ + -device gen16b-s390x-cpu,drawer-id=1,book-id=1,socket-id=2,core-id=2 \ + -device gen16b-s390x-cpu,drawer-id=1,book-id=1,socket-id=2,core-id=3 \ + \ + -device gen16b-s390x-cpu,drawer-id=0,book-id=0,socket-id=0,core-id=9 \ + -device gen16b-s390x-cpu,drawer-id=0,book-id=0,socket-id=0,core-id=14 \ + \ + -device gen16b-s390x-cpu,core-id=4,dedicated=on,entitlement=high + +The entitlement defined for the CPU 4 will only be used after the guest +successfully enables vertical polarization by using the PTF instruction. diff --git a/docs/system/target-s390x.rst b/docs/system/target-s390x.rst index f6f1143..94c981e 100644 --- a/docs/system/target-s390x.rst +++ b/docs/system/target-s390x.rst @@ -34,3 +34,4 @@ Architectural features .. toctree:: s390x/bootdevices s390x/protvirt + s390x/cpu-topology diff --git a/qapi/machine.json b/qapi/machine.json index b4bd26f..6c9d2f6 100644 --- a/qapi/machine.json +++ b/qapi/machine.json @@ -909,6 +909,8 @@ # Which members are optional and which mandatory depends on the # architecture and board. # +# For s390x see :ref:`cpu-topology-s390x`. +# # The ids other than the node-id specify the position of the CPU # within the CPU topology (as defined by the machine property "smp", # thus see also type @SMPConfiguration) |